PHP了解回调 - preg_replace_callback（）和preg_match_all（）之间的区别

Question

I am a bit confused on the use of preg_replace_callback()

I have a $content with some URLs inside .

Previously I used

 $content = preg_match_all( '/(http[s]?:[^\s]*)/i', $content, $links );


 foreach ($links[1] as $link ) {
            // we have the link. find image , download, replace the content with image
            // echo '</br>LINK : '. $link;
            $url = esc_url_raw( $link );
            $url_name = parse_url($url); 
            $url_name = $description = $url_name['host'];// get rid of http://..
            $url = 'http://somescriptonsite/v1/' .  urlencode($url)   . '?w=' . $width ;
            } 

    return $url;

But what I really need is to REPLACE the original URL with my parsed URL...

So I tried the preg_replace_callback:

function o99_simple_parse($content){

$content = preg_replace_callback( '/(http[s]?:[^\s]*)/i', 'o99_simple_callback', $content );


return $content;
}

and :

function o99_simple_callback($url){
    // how to get the URL which is actually the match? and width ??
        $url = esc_url_raw( $link );
        $url_name = parse_url($url); 
        $url_name = $description = $url_name['host'];// get rid of http://..
        $url = 'http://something' .  urlencode($url)   . '?w=' . $width ; 
        return $url; // what i really need to replace 
    }

I assumed that the callback will work in a way that EVERY match will call the callback (recursively ?) and get back results , thus allowing for to replace on-the-fly the URLS in $content with the parsed $url from o99_simple_callbac() .

But another question here (and especially this comment ) triggered my doubts .

If the preg_replace_callback() actually pass the whole array of matches , then what is actually the difference between what I used previously ( preg_match_all() in first example ) and the callback example ?

What am I missing / misunderstanding ?? What would be the correct way of replacing the URLS found in $content with the parsed urls ?

Answer 1

The other answers may have been sufficient, but let me give you one more take using a simpler example.

Let's say we have the following data in $subject ,

RECORD Male 1987-11-29 New York
RECORD Female 1987-07-13 Tennessee
RECORD Female 1990-04-14 New York

and the following regular expression in $pattern ,

/RECORD (Male|Female) (\d\d\d\d)-(\d\d)-(\d\d) ([\w ]+)/

Let's compare three approaches.

preg_match_all

First, the vanilla preg_match_all :

preg_match_all($pattern, $subject, $matches);

Here's what $matches comes out to be:

Array
(
    [0] => Array
        (
            [0] => RECORD Male 1987-11-29 New York
            [1] => RECORD Female 1987-07-13 Tennessee
            [2] => RECORD Female 1990-04-14 New York
        )

    [1] => Array
        (
            [0] => Male
            [1] => Female
            [2] => Female
        )

    [2] => Array
        (
            [0] => 1987
            [1] => 1987
            [2] => 1990
        )

    [3] => Array
        (
            [0] => 11
            [1] => 07
            [2] => 04
        )

    [4] => Array
        (
            [0] => 29
            [1] => 13
            [2] => 14
        )

    [5] => Array
        (
            [0] => New York
            [1] => Tennessee
            [2] => New York
        )

)

Whether we're talking about the gender field in my example with the URL field in your example, it's clear that looping through $matches[1] iterates through just that field:

foreach ($matches[1] as $match)
{
    $gender = $match;
    // ...
}

However, as you noticed, changes you make to $matches[1] , even if you iterated through its subarrays by reference, do not reflect in $subject , ie you cannot perform replacements via preg_match_all .

preg_match_all with PREG_SET_ORDER

Before we jump into preg_replace_callback though, let's take a look at one of preg_match_all 's commonly used flags, PREG_SET_ORDER .

preg_match_all($pattern, $subject, $matches, PREG_SET_ORDER);

This outputs something (seemingly) completely different!

Array
(
    [0] => Array
        (
            [0] => RECORD Male 1987-11-29 New York
            [1] => Male
            [2] => 1987
            [3] => 11
            [4] => 29
            [5] => New York
        )

    [1] => Array
        (
            [0] => RECORD Female 1987-07-13 Tennessee
            [1] => Female
            [2] => 1987
            [3] => 07
            [4] => 13
            [5] => Tennessee
        )

    [2] => Array
        (
            [0] => RECORD Female 1990-04-14 New York
            [1] => Female
            [2] => 1990
            [3] => 04
            [4] => 14
            [5] => New York
        )

)

Now, each subarray contains the set of capture groups per match , as opposed to the set of matches , per capture group . (In yet other words, this is the transpose of the other array.) If you wanted to play with the gender (or URL) of each match, you'd now have to write this:

foreach ($matches as $match)
{
    $gender = $match[1];
    // ...
}

preg_replace_callback

And that's what preg_replace_callback is like. It calls the callback for each set of matches (that is, including all its capture groups , at once), as if you were using the PREG_SET_ORDER flag. That is, contrast the way preg_replace_callback is used,

preg_replace_callback($pattern, $subject, 'my_callback');
function my_callback($matches)
{
    $gender = $match[1];
    // ...
    return $gender;
}

to the PREG_SET_ORDER example. Note how the two examples iterate through matches in exactly the same way, the only difference being that preg_replace_callback gives you an opportunity to return a value for replacement.

Answer 2

It does not pass all matches, but invokes the callback for each match. The callback won't receive a single string parameter, but a list of strings. $match[0] is the whole match, and $match[1] the first capture group (what's in your regex between the first parens).

So this is how your callback should look:

function o99_simple_callback($match){
    $url = $match[1];
    //$url = esc_url_raw( $link );
    $url_name = parse_url($url); 
    $url_name = $description = $url_name['host'];// get rid of http://..
    $url = 'http://something' .  urlencode($url)   . '?w=' . $width ; 
    return $url; // what i really need to replace 
}

Please also see the manual examples on preg_replace_callback

Answer 3

preg_replace_callback

1. Using preg_replace_callback() to Replace Patterns
2. Generating replacement strings with a callback function
3. Generating replacement strings with an anonymous function